The sensitivity of sister chromatid exchanges (SCE) in response to mutagens will be extended to short-term peripheral lymphocyte cultures. The purpose being to assess the likely advantages to stem from this procedure to monitor chronic exposures of test animals to low levels of mutagen and the introduction of suspected co-factors. The feasibility of conducting mutagen and carcinogen assays on the same target cell population and the same animal is presented by the autoimmune-prone Armenian hamster, Cricetulus migratorius (2n equals 22). Unless exposed to nitroso compounds to induce angioimmunoblastic lymphadenopathy (AIL) and immunoblastic sarcoma (IBS), the Armenian hamster remains characteristically tumor-free throughout a lifespan of 1,000 days. This contrasts sharply with the Chinese hamster, Cricetulus griseus (2n equals 22) which fails to respond to MNU (70 mg/k body weight) when administered intravenously. In addition, clinical and epidemiological considerations have now clearly associated therapeutic regimes and environmental exposures to pesticide as co-factors for the precipitous onset of clinical AIL/IBS, notably in segments of the human population with recognized autoimmune-related disorders. Animal studies will attempt to simulate recognized episodes associated with clinical AIL. Monitoring low-level chronicity tests comprised of threshold levels of two or more suspected co-factors can only be achieved by the adaptation of the peripheral lymphocyte for the sensitivity provided by the SCE test.